How to Smoke a Prime Rib: The USDA Numbers, and What They Do Not Cover

A rib roast is the most expensive thing most people will ever put in a smoker, and it is usually cooked once a year. So it is worth knowing exactly which numbers are published and which ones are someone's guess.

The published table

USDA's holiday roasting chart gives these for beef rib roast, in an oven at 325°F:

Turned into hours, by our arithmetic from that rate:

A boneless 4 lb roast at 39–43 minutes a pound is 2h 36m–2h 52m, longer than a bone-in roast of the same weight. USDA's explanation: boned and rolled meat takes longer per pound because the heat has further to go through solid meat.

What the table does not cover: a low smoker

That chart is for an oven at 325°F. USDA's smoking guidance is a different document, and it says to keep the smoker's air between 225 and 300°F.

So:

• If your smoker holds 325°F, the table above is the closest published reference there is. Using it for a smoker is our inference, not USDA's.
• At 225 to 275°F, the roast will take longer. By how much is not something anyone has published for rib roast, so this page does not print a number.

That is why the thermometer matters more than the clock on this cut.

The temperature question

USDA's figure for beef roasts is a minimum of 145°F, measured with a food thermometer, then at least three minutes of rest before carving. It says you may choose to cook higher for personal preference.

Many prime rib recipes pull the roast well below that, for rare or medium-rare. Those targets are below the USDA minimum. This page reports the USDA figure and does not recommend going under it.

Two thermometers

USDA's smoking guidance asks for two: one for the air in the smoker, one for the meat. On a roast this expensive, a leave-in probe that alarms before the target is the difference between checking once and opening the lid every twenty minutes.

The lid thermometer on most cookers reads the air at the top of the dome, not at the grate where the roast is. Put a probe at the grate.

Wood

Beef takes strong smoke well, and a rib roast is on for a few hours, not twelve. A few chunks of hickory or oak are plenty. Which wood does what, in one chart.

Afterwards

USDA says refrigerate leftovers within 2 hours, and use them within 4 days or freeze them.

Planning the day

Work backwards from dinner. Take the long end of the table, add the rest and the time to get the smoker steady, and light it then. If the roast is early, it holds; if it is late, there is nothing you can do but wait. The smoker calculator does the counting for the cuts it covers, and how to smoke a ham covers the other holiday roast.